“Even mild to moderate amounts of exercise appear to protect against kidney stone formation,” said lead investigator Mathew Sorensen, MD, of the University of Washington Medical Center in Seattle. “It is not the intensity of the activity that appears to matter; it's the amount of activity.”

He and his colleagues analyzed data from 84,225 postmenopausal women aged 50-79 enrolled 1993-1998 in the Women's Health Initiative (WHI) Observational Study who had no history of kidney stones and had filled out the WHI food frequency questionnaire. Women reported kidney stone development annually with a median follow-up of eight years.

Incidence kidney stones were reported by 2,392 women (2.8%). Women in the lowest physical activity category had a 14% decreased risk of kidney stones compared with sedentary women in adjusted analyses. Moreover, as weekly activity increased, the investigators observed up to a 31% decreased risk of kidney stones. Intensity of activity was not associated with stone formation, according to the researchers. The study also showed that greater dietary energy intake was associated with up to a 44% increased risk of incident kidney stones. Lower dietary energy intake, however, did not protect against stone formation. Greater body mass index category increased the risk of incident stones.

For women to get the maximum benefit in terms of lowering stone risk, they would need to engage in a modest amount of physical activity, such as three hours of leisurely walking at about two to four miles per hour or four hours of gardening in a week, Dr. Sorensen said. “We're not talking about running a marathon,” he said.